Responses of photosynthetic characters of Skeletonema costatum to different nutrient conditions

The photosynthetic capacity of phytoplankton is frequently limited by the availability of nutrients. To explore the mechanism of the effect of nutrient availability on photosynthesis, batch cultures of a marine diatom Skeletonema costatum (Greville) Cleve were carried out under different nitrate (N: 0-220.75 mu M) and phosphate (P: 0-9.075 mu M) concentrations. Changes of photosynthetic characters, including the photosynthetic rate (measured by O-2 evolution) and the rbcL mRNA content (encoding the large subunit of the Calvin cycle enzyme, RuBisCO), were both studied. Within the range tested, both the photosynthetic rate and rbcL transcript levels correlated significantly with N and P concentrations in the medium. Additionally, the photosynthetic rates and rbcL transcript levels were both growth dependent. Significant correlations were also found between the abundance of rbcL mRNA and the photosynthetic rate (R-2 = 0.800), rbcL and growth rate (R-2 = 0.855), the photosynthetic rate and growth rate (R-2 = 0.815). These results are consistent with N and P nutrition-regulating photosynthesis from the transcriptional levels of rbcL. The rbcL transcript level has the potential to be a good marker of algal growth and primary productivity.